Abstract: The main task of mechanical analyses on over constraintmechanism is the solution of the compatibility equation of distortion, but itis difficult to obtain the solution directly because its direct kinematics is not completely established. A method to solve the compatibility equation ofdistortion indirectly is put forward based on the kinematic constraint relation. Theprinciple and the complete procedures about theplanar and the space mechanisms are given, respectively. The resultsshow that the method is effective especially for complicatedover constraint parallel manipulator. At last, how to use the method to solvethe multi-degree over constraint mechanism is discussed.